lindberg et ai



ug- 31, 1954 A. w. LINDBERG x-:rAL 2,688,108

ELECTRONIC SPARK GENERATOR Filed Oct. 5, 1951 /Na/ENTo/as: @LL/JN W.LINDBEIPG, JAMES C. ROMBACH,

Patented Aug. 31, 1954 ELECTRONIC SPARK GENERATOR Allan W. Lindberg,Webster Groves, and James C. Rombach, Rock Hill, Mo., assignors toMissouri Automatic Control Corporation, St. Louis, Mo., a corporation ofMissouri Application October 5, 1951, Serial No. 249,852

2 Claims. 1

This invention relates generally to spark ignition devices and moreparticularly to an eleotronc spark ignitor capable of producingcontinued arcing of suitable strength and size so as to be, for example,a reliable ignition means for pressure spray-type oil burners.

The usual spark ignition devices used in connection with oil burnersemploy a massive and costly transformer having a high ratio of secondaryto primary winding in order to develop the sufficiently high voltagenecessary to produce a spark adequate for the purpose. In the presentinvention, it is the primary object to provide a generally new andimproved spark ignition device suitable for oil burner ignition use, inwhich a substantial saving in cost, and use of materials in criticallyshort supply, is achieved and in which a substantial reduction in weightis accomplished.

A further object of the invention is to provide a spark ignition devicein which sufficiently high potential to produce a satisfactory arc isobtained by supplying energy to a relatively small transformerintermittently and cutting off the supply abruptly at the termination ofeach interval without the use of mechanical motion or make and breakcontacts.

A further object is to provide a, spark generator as above capable ofproducing continuous arcing at high frequency and of such strength as tobe suitable for oil burner ignition.

More specifically, it is an object to provide an oscillator sparkgenerator circuit having a transformer winding in the plate circuit of agridcontrolled electron discharge tube and a feedback from transformerto grid, in which the circuit oscillates free from the flywheel effector circuit resonance so as to permit the flow of current in thetransformer winding to be cut off sharply at maximum tube output uponreversal of the feedback signal at tube saturation, thereby to providean unusually high induced voltage for bridging a spark gap.

These and other objects and advantages will appear from the followingcomplete description when read in connection with the accompanyingdrawing.

The single ligure of the drawing is a diagrammatic illustration of aform of the present invention.

Referring to the drawing, numeral l generally (Cl. S15-206) indicates anelectron tube which is preferably a high vacuum pentode having a plate II, a suppressor grid I2, a screen grid I3, a control grid I4, a cathodeI5, and a cathode heater IB. A transformer is generally indicated at Il,having a primary winding I E series connected in the plate circuit oftube I0. Connected across the primary winding i8 is a spark-gap circuitincluding a transformer secondary winding I9 and a pair of spacedelectrodes (spark-gap) 20 and 2|. The suppressor grid I2 is internallyconnected to the cathode I 5 and the screen grid I3 is connected to thecircuit power supply ahead of the transformer I l. The cathode heater IBmay be supplied energy in any suitable manner as by a small transformer(not shown).

A low impedance feedback to tube I0 is provided by a winding 22 which isin inductive relation with transformer primary winding I8 and isconnected to the control grid I4. A resistor 23 is included in theconnection between winding 22 and the control grid so as to limit thecurrent flow through the control grid cathode circuit to a value whichmay be safely carried by the grid.

The power supply to the above circuit is shown as being a volt, 60cycle, A. C. commercial source supplied through leads 24 and 25, whichis half-wave rectified by the provision of a selenium rectier 2t andfiltered by the provision of an inductance 2'! and capacitors 28 and 29.While this power supply provides a satisfactory arc for the purpose, itwill be understood that the slight additional cost of full-waverectcation will produce a stronger are at 2li-2 I. In order to providean unusually high induced voltage in the transformer primary winding I9,any lumped capacitance has been avoided, the circuit generally beingdesigned with a view to reducing capacitance to a minimum and thewindings IB, I9, and 22 have been designed with relation to thedischarge tube characteristics so that oscillation of the circuit due tointeraction between output and feedback occurs at a frequencyconsiderably below the resonant frequency of the circuit. With thisarrangement, the cut-off of current flow through the transformer, whichoccurs at tube saturation, will be sharp and not rounded off in theusual sine wave form, which would otherwise occur if thel circuitincluded appreciable capacitance and were oscillating at resonantfrequency.

The use of a single high vacuum pentode tube provides the high outputnecessary to produce a strong arc, and while a triode may, of course, besubstituted for a pentode, it is doubtful that the output of a singletriode would be sufcient at the plate voltage of the usual 110 voltsupply to provide the strength of arc necessary for dependable ignitionof oil burners.

I n operation In starting, the control grid potential is Zero, therebeing no bias. When the cathode I5 becomes sufliciently heated, the tubeiii begins to discharge and a now of current through the plate circuitbegins, also starting from zero. As current starts to ow through theplate circuit, this change causes a voltage to be induced in thefeedback winding 22 resulting in a positive charge on the control grid.This positive feedback to the control grid further increases the tubedischarge and consequently the plate current. The interaction iscumulative and, there being no limiting or bias of the control grid theplate current rises to the point of maximum tube discharge, the platevoltage being adequate. When maximum tube discharge is reached, the rateof increase of current flow through winding i8 stops and, consequently,the feedback to the control grid drops to zero.

The drop in positive grid potential results in a descrease in tubedischarge and plate current. As the plate current decreases, thepolarity of the induced feedback is reversed and the control gridrapidly becomes strongly negative, driving the tube beyond cut-off. Thisreversal from a strong positive to a strong negative grid occurs, ofcourse, very rapidly at the point where tube output ceases to increasebecause of the cumulative interaction of decreasing plate current anddecreasing signal. As a result of this abrupt collapse of plate current,a high potential is self-induced in the primary Winding It and a highpotential is induced in the secondary winding i9 by mutual induction.The inductances I3 and I9 being series connected across the spark gapelectrodes 20--2 l the sum of these potentials draws an arc across theelectrodes suitable for the purpose. When the energy in coils i8 and I9is dissipated by the arc, the circuit relaxes, the control gridpotential returns to zero, and the circuit is ready to repeat the cycle.

The waveform of the current supplied to the transformer is therefore notsinusoidal but rather of general saw-tooth form. By delivering energy tothe transformer in this manner, energy is delivered in increasing valueand stored throughout for the greater part of the cycle and theprecipitous cut-Dif, which ends the cycle, results in an extremely highinduced voltage for bridging the spark gap. While some distributedcapacitance in the inductances of the circuit is unavoidable, thecircuit is, nevertheless, designed so that the frequency at which thecircuit cycles due to the interaction between output and feedback neverapproaches the resonant frequency of the circuit. The grid circuithaving low impedance, the grid returns to Zero quickly.I

By way of example, the following values were used in the illustratedcircuit with l1() volt, halfwave, rectied input current and resulted ina satisfactory arc for ignition of oil burners occurring at a frequencyof approximately 1800 cycles per second.

Electron tube I|J=a commercial 6AU5 pentode.

TRANSFORME R DATA Feedback Winding 22, 200 turns Secondary Wind- PrimaryWinding 18,

667 turns ing 19, 714 turns Ind. =0.3 henry Res. =220 ohms Ind. :0.029henry Inductance=-3 henry Res. =2 ohms l' 10 Resistance-3o ohms Mutualinduetances Winding I8 to I9=0.27 henry Winding I8 to 22:0.09 henryWinding I9 to 22:0.07 henry The resistor 23:1000 ohms.

It is to be understood that the characteristics and frequency ofoccurrence of the resulting ignition spark can be varied by the use ofother types of electron discharge tubes and by other values of theinductances and resistor than those set forth hereinabove by way ofexample. The foregoing is, therefore, intended to be illustrative 25 andnot limiting, the scope of the invention being set forth in the appendedclaims.

I claim: 1. A spark generator circuit comprising a transformer having aprimary and secondary winding, a pair of leads for connection with asource o'f power, a grid-controlled electron discharge tube seriesconnected with said primary winding across said. leads, a pair of spacedelectrodes having such circuit connections with said transformer thatpotential induced in said transformer secondary winding is impressed onthe air gap between them, and a feedback winding in inductiverelationship with said primary winding and having one side thereofconnected to the tube cathode, the capacitance of the circuit beingsufficiently low and the relationship of the constants of the externalelements of the circuit to the constants of the tube being such thatsaid circuit oscillates freely due to interaction between output andfeedback at a frequency substantially below the resonant frequency ofthe circuit.

2. A spark generator circuit comprising a transformer having a primarywinding and a secondary winding, a pair of spaced electrodes seriesconnected with said secondary winding across said primary winding, apair of leads for connection with a source of power, a grid-controlledelectron discharge tube series connected with said primary windingacross said leads, and a feedback winding in inductive relationship withsaid primary winding and having one side thereof connected to the tubecontrol grid and its other side connected to the tube cathode, saidcircuit being so designed as to reduce the capacitance therein to apoint wherein the cut-off of current flow through said transformer dueto interaction between feed back and tube output is abrupt and notappreciably affected by carry-over due to capacitive reactance,

References cited in the sie of this patent UNITED STATES PATENTS NumberName Date 1,589,489 Snook June 22, 1926 0 2,347,286 saneren@ Apr. 25,1944

